Process for the production of a ferrochrome-silicon-aluminum alloy



Patented Mar. 17, 1953 PR6OES sea THE PB ROGHROME-SILICON- Au us estimates it Fina ALUMINUM ALLOY Kuhlmann, Niagara Falls; N;- Y., as-' si ns to Union Carbide and Carbon Corporatioii, a' corporation of New York NdDrawiiig.

Application January 10, 1952,

Serial No. 265,924 seams. (01. 75-135) fhe invention relatesto a; methodfor the P 30,- duction of a v ferrochromium sneon-aluminum alloy containingbetween 5%- and 25% alu- The ferrochromium silicon -aluminum alloys produced according to this invention are particularly useful in the production of low-carbon ferrochromium or chromium steels by thereduction of chromium cre or chromium-bearin slags. n I I Alloys of this type maybe prepared by alloying aluminum metal with molten ferrochromium-silicon or by carbon reduction with a mixture of ferrochromium, quartzite and clay or bauxite. In the first process" it is necessary to employ metallic aluminum. In the second, the use of clay or bauxite introduces undesirable iron as well as hydrated water which consumes extra reducing agent and power;

It is the primary object of the present invention to provide a process for the production of a ferrochromium-silicon-aluminum alloy of low-carbon and between 5% and 25% aluminum content wherein no metallic aluminum need be added.

Another object is to produce such an alloy with a minimum of slag formation thereby increasing the recovery of chromium from the raw materials employed.

A still further object is to eliminate the expense of using clay or bauxite as the source of alumina.

Broadly the invention comprises a process for the production of a low-carbon ferrochromiumsilicon-aluminum alloy which contains between 5% and 25% aluminum by the complete carbon reduction of chromite and quartzite. Magnesia and alumina are present in the chromite generally used for the production of chromium alloys, alumina usually being present in amounts varying from upward. In process of the invention, the gangue constituents of the chromite are reduced, including the magnesia, which is volatilized, thus making the reduction of the bulk of the alumina in the charge possible. Carbon for the reduction may be supplied in any of several forms. Coal and wood chips are an excellent source of carbon. A portion of the carbon may also be supplied as highcarbon ferrochromium or coke. The reduction may be carried out in a conventional electric arc smelting furnace. In this process the major proportion of the aluminum of the resulting alloy is supplied by reduction of the alumina in the chromite and a minor proportion by the reduction of the alumina in the quartzite and ash of the carbon reducing agent. To obtain an aluminumcontent the alloy of from 5% to v 25%, the materials charged into the furnace are properly balancediaccor'ding to" the well established practice of the art.

The following specific examples of the application of the method of the invention to the production of low-carbon chromium-siliconaluminum alloys illustrate the principles and operation of the invention.

alloy containing about 33% chromium, 40 silicon; 9% aluminum; less than 0.1% carbon; remainder, substantially all iron was prepared by electric furnace smelting of a mixture containingi Parts by weight Quartzite' 750 Chromium ore High-carbon ferrochrom Pocahontas coal Wood chips The; high-carbon",ferrochromium in the above mixture contained approximately chromium, 7% silicon and 6% carbon. The chrome ore analyzed:

Per cent CrzOc 36.38 FeO 13.53 A1203 26.90 SiOz 4.15 MgO CaO 17.48

The amount of carbon fed was practically the theoretical amount required to reduce all of the oxides in the charge, including the magnesia in the ore, the bulk of which was volatilized as magnesium during the smelting operation. Since the gangue of the ore was almost completely reduced very little slag was produced. In the method of the invention, the ratio of chromium ore to high-carbon ferrochromium may be varied to suit the requirements for alloy composition and the analysis of the particular ore employed.

Chromium ore may, if desired, be used as the sole source for both the aluminum and chromium of the resulting alloy as shown in the example below. In this example an alloy containing about 38% chromium, 28% silicon, 8% aluminum, less than 0.1% carbon, remainder substantially all iron was prepared by electric furnace smelting of a mixture containing;

Parts by weight Wood chips The chromium ore in the charge analyzed:

Per cent C12O3 43.56 FeO 24.00 A1203 15.57 SiOz 4.64 MgO CaO 10.22

Other alloys produced according to the process of the invention have the following approximate analyses: 38% chromium, 42% silicon, 5% aluminum, 0.2% carbon, remainder substantially all iron; and 22% chromium, 40% silicon, 22% aluminum, 0.03% carbon, remainder substantially all iron.

Since practically no slag is produced in the method of the invention, the recovery of chromium is higher than in processes wherein the gangue of the ore must be fluxed to produce a slag. Also both theoretical studies and practical tests have demonstrated that under usual commercial conditions it is more economical to obtain aluminum from the complete carbon reduction of chromium ore using power and reducing agent to volatilize the magnesia than to prepare the alloys from clay or bauxite and highcarbon ferrochromium.

Alloys made according to the invention may contain some calcium in addition to chromium, silicon, aluminum and iron. The amount of calcium present is dependent upon the concentration of lime in the raw materials or the amount of limestone or limeadded to the charge. The presence of calcium in the alloy has been found to be beneficial in the application in which the alloy is generally employed.

A Vchromium-silicon-a1uminum alloy which may be made by the method of this invention is claimed in a co-pending application, Serial No. 88,681, filed April 20, 1949, now Patent No. 2,608,482 in the name of Joseph H. Brennan.

This application is a continuation-in-part of application Serial No. 88,684, filed April 20, 1949, now abandoned.

What is claimed is:

1. Process for the production of a low-carbon chromium-silicon-aluminum alloy containing from 5% to 25% aluminum which comprises preparing a charge of raw materials containing chromium ore and silica with a balanced addition of carbonaceous reducing agent in a stoichiometrical amount sufiicient to reduce all oxides in said charge including the ash of said reducing agent; said chromium ore containing magnesia and alumina; the total alumina present in the materials charged being in an amount sufiicient to impart to the alloy an aluminum content of between 5% and 25%; smelting said charge until substantially all magnesia in said raw materials is reduced and volatilized from said charge; continuing said smelting operation until substantially all the alumina in said raw materials is reduced to aluminum; and tapping the low-carbon chromium-silicon-aluminum alloy produced in said smelting operation.

2. Process as claimed in claim 1 wherein a portion of the carbonaceous reducing agent is supplied in the form of high-carbon ferrochromium.

3. Process as claimed in claim 1 wherein said chromium ore is chromite.

AUGUST M. KUHLMANN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. PROCESS FOR THE PRODUCTION OF A LOW-CARBON CHROMIUM-SILICON-ALUMINUM ALLOY CONTAINING FROM 5% TO 25% ALUMINUM WHICH COMPRISES PREPARING A CHARGE OF RAW MATERIALS CONTAINING CHROMIUM ORE AND SILICA WITH A BALANCED ADDITION OF CARBONACEOUS REDUCING AGENT IN A STOICHIOMETRICAL AMOUNT SUFFICIENT TO REDUCE ALL OXIDES IN SAID CHARGE INCLUDING THE ASH OF SAID REDUCING AGENT; SAID CHROMIUM ORE CONTAINING MAGNESIA AND ALUMINA; THE TOTAL ALUMINA PRESENT IN THE MATERIALS CHARGED BEING IN AN AMOUNT SUFFICIENT TO IMPART TO THE ALLOY AN ALUMINUM CONTENT OF BETWEEN 5% AND 25%; SMELTING OPERATION UNTIL SUBSTANSUBSTANTIALLY ALL MAGNESIA IN SAID RAW MATERIALS IS REDUCED AND VOLATILIZED FROM SAID CHARGE; CONTINUING SAID SMELTING OPERATION UNTIL SUBSTANTIALLY ALL THE ALUMINA IN SAID RAW MATERIALS IS REDUCED TO ALUMINUM; AND TAPPING THE LOW-CARBON CHROMIUM-SILICON-ALUMINUM ALLOY PRODUCED IN SAID SMELTING OPERATION. 